The present invention relates to machines for stacking and unstacking articles such as baking pans and the like. More particularly, the invention relates to a system and the mechanism therein for selective operation in a pan unstacking mode and in a pan pass-through mode and in a pan stacking mode, and including elevator means for moving a stack of pans incrementally upwardly to a stacking-unstacking station during an unstacking operation as pans are removed from the top of the stack, and for incrementally moving a stack of pans downwardly away from the stacking-unstacking station during a stacking operation as pans are added to the top of the stack.
A machine for performing the stacking and unstacking functions is disclosed in detail in the aforementioned U.S. Application Ser. No. 339,314, and separate machines for respectively performing stacking and unstacking operations are disclosed in the U.S. Pat. No. 3,770,143, issued to J. J. Breitbach on Nov. 6, 1973 and entitled "Apparatus For Transferring Trays Between A Conveyor System And A Stack". In such prior art systems it is important that during the stacking and unstacking operations, and particularly the latter, the stack of pans be properly positioned on the elevator so as to be in proper alignment with the stacking-unstacking station, in order to insure proper operation of the stacking and unstacking apparatus, and in order to insure accurate positioning of the pans on an outfeed conveyor as they are unstacked. However, the prior art systems include no means for insuring the proper alignment of the pan stack with respect to the stacking-unstacking station.